JP2009215978A - Fuel direct injection engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cool a circumference direction whole zone of a piston homogeneously while improving combustion conditions by homogeneously mixing fuel and air in the circumference direction whole zone of a cavity in a fuel direct injection engine provided with the vent roof type piston. <P>SOLUTION: When the cavity 25 recessed at a center part of a top surface of a piston 13 divided into N units of imaginary cavity divisions, mixing state of fuel and air can be homogenized by making volume of each imaginary cavity division roughly same. A cooling channel 26 to which oil is supplied is provided at a reverse part of the cavity 25 in a circumference direction, and height of the cooling channel 26 is changed in the circumference direction so as to keep the minimum distance "d" between the cavity 25 and the cooling channel 26 roughly constant in the circumference direction. Consequently, cooling conditions of the cavity 25 become constant in each imaginary cavity division, and combustion conditions of air fuel mixture in the cavity 25 can be further homogenized. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piston in which the height of the top surface in the piston central axis direction changes in the circumferential direction, a cavity recessed at the center of the top surface of the piston, and a fuel injector that injects fuel into the cavity. And a fuel direct injection engine.

  The shape of the cavity formed on the flat top surface of the piston of the direct fuel injection engine is reduced by increasing the diameter of the cavity in the fuel injection direction from the fuel injector, and in the direction other than the fuel injection direction. By increasing the depth by reducing the diameter, the distance between the cooling channel and the cavity is made constant in the circumferential direction by making the annular cooling channel formed inside the piston undulate. A device that achieves uniform cooling is known from Patent Document 1 below.

In addition, an annular cooling channel along the outer periphery of the cavity and an oil passage extending in the direction of the piston center axis on the intake and exhaust sides of the piston pin hole of the piston boss are formed inside the pent roof type piston of the direct fuel injection engine. Patent Document 2 below discloses that the oil passage is communicated with the cooling channel and further extended to the piston top surface side to achieve uniform cooling of the entire piston.
No. 1-22168 JP 2007-278251 A

  By the way, in the direct fuel injection engine described in Patent Document 2 having a pent roof type piston, in order to efficiently cool the vicinity of the ridge line portion of the piston top surface where the distance from the cooling channel becomes large, the piston is in the axial direction of the piston. The extended oil passage extends beyond the cooling channel to the piston top surface, which not only complicates the internal structure of the piston and increases the processing cost, but is also sufficient because the upper end of the oil passage is a bag path It was not possible to supply a sufficient amount of oil, and it might be difficult to achieve uniform cooling of the entire piston.

  The present invention has been made in view of the above circumstances, and in a fuel direct injection engine equipped with a pent roof type piston, fuel and air are uniformly mixed throughout the circumferential direction of the cavity to improve the combustion state. It aims at enabling it to cool uniformly the whole circumferential direction of a piston.

  In order to achieve the above object, according to the invention described in claim 1, a piston whose top surface in the direction of the central axis of the piston changes in the circumferential direction, and a concave portion in the center of the top surface of the piston. In a direct fuel injection engine having a cavity and a fuel injector for injecting fuel into the cavity, N is a natural number of 2 or more, and extends radially from the inner wall surface of the cavity and the central axis of the piston. The cavity is divided into N virtual cavity sections with N half planes having equal sandwiching angles with each other so that the volumes of the virtual cavity sections are substantially equal. In addition to setting the shape of the inner wall surface of the piston, a cooling channel for supplying oil to the back of the cavity in the piston is provided in the circumferential direction. The direct fuel injection engine, wherein the height of the cooling channel in the piston central axis direction is changed in the circumferential direction so that the shortest distance between the cavity and the cooling channel is substantially uniform in the circumferential direction. Is proposed.

  According to the invention described in claim 2, in addition to the configuration of claim 1, a direct fuel injection engine is proposed in which the cross-sectional shape of the cooling channel is substantially the same in the circumferential direction. .

  According to a third aspect of the present invention, in addition to the configuration of the first aspect, the height of the piston central axis direction of the lower portion of the cooling channel is substantially the same in the circumferential direction. A direct injection engine is proposed.

  According to the invention described in claim 4, in addition to the configuration of any one of claims 1 to 3, the height of the upper portion of the cooling channel in the direction of the piston central axis is the height of the piston pin axis. Oil supply that extends downward from an inclined portion that is highest in the direction, lowest in the direction orthogonal to the piston pin axis, and monotonically changing between the two directions, the height of the cooling channel changing There is proposed a direct fuel injection engine characterized in that oil is injected from an oil jet provided below a piston into a passage.

  According to the invention described in claim 5, in addition to the structure of claim 3, the cooling channel is configured by a hollow pipe, and a wear-resistant ring for holding the piston ring is integrally formed on the outer peripheral surface thereof. A featured fuel direct injection engine is proposed.

  According to the invention described in claim 6, in addition to the structure of any one of claims 1 to 4, the cooling channel is separated into two cooling channels with the piston pin axis interposed therebetween. A direct fuel injection engine is proposed in which oil is supplied from one end of each cooling channel and discharged from the other end.

  The pressure ring 31 of the embodiment corresponds to the piston ring of the present invention.

  According to the configuration of claim 1, when the cavity recessed in the central portion of the top surface of the piston is partitioned into N virtual cavity sections, the volume of each virtual cavity section is substantially equal. Since the shape of the inner wall surface of the cavity is set, the fuel and air mixing state in the cavity can be made uniform to improve engine output and reduce harmful exhaust substances. In addition, when the cooling channel for supplying oil to the back of the cavity is provided in the circumferential direction, the piston in the central axis direction of the piston of the cooling channel is set so that the shortest distance between the cavity and the cooling channel is substantially uniform in the circumferential direction. Since the height is changed in the circumferential direction, the cooling state of the cavities becomes substantially equal in each virtual cavity section, and the combustion state of the air-fuel mixture in the cavities can be made more uniform.

  According to the second aspect of the present invention, since the cross-sectional shape of the cooling channel is substantially the same in the circumferential direction, the oil flow rate in each part of the cooling channel is constant, and the piston is cooled more uniformly in the circumferential direction. be able to.

  According to the third aspect of the present invention, since the height of the lower portion of the cooling channel in the central axis direction of the piston is substantially the same in the circumferential direction, the flow of the fuel can be promoted by reducing the undulation of the cooling channel. In addition, the lower part of the core for forming the cooling channel during casting of the piston can be flattened to facilitate the manufacture of the core and the support of the core in the mold.

  According to the fourth aspect of the present invention, the height of the upper portion of the cooling channel in the direction of the piston central axis is highest in the direction of the piston pin axis, lowest in the direction orthogonal to the piston pin axis, and the two The oil jet is injected from the oil jet provided below the piston into the oil supply passage extending downward from the inclined portion where the height of the cooling channel changes, and the oil jet from the oil jet to the oil. Since the fuel injected into the supply passage is supplied to the inclined portion of the cooling channel, most of the fuel flows into the higher side of the cooling channel that forms an obtuse angle with respect to the oil supply passage. As a result, the flow direction of the fuel in the cooling channel can be made constant, and the cooling of the piston can be stabilized.

  According to the fifth aspect of the present invention, since the wear-resistant ring for holding the piston ring is integrally formed on the outer peripheral surface of the cooling channel constituted by the hollow pipe, the wear-resistant ring is used without using the core when casting the piston. Thus, a cooling channel can be formed. At this time, since the height of the lower part of the cooling channel in the piston central axis direction is substantially the same in the circumferential direction, the formation of the wear-resistant ring is not hindered.

  According to the configuration of claim 6, the cooling channel is separated into two cooling channels with the piston pin axis in between, oil is supplied from one end side of each cooling channel, and oil is discharged from the other end side. Unlike the annular cooling channel, there is only one flow path from the oil inlet to the outlet, and the oil flow in the cooling channel is stabilized.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1 to 14 show a first embodiment of the present invention. FIG. 1 is a longitudinal sectional view of a main part of a diesel engine (a sectional view taken along line 1-1 of FIG. 12), and FIG. FIG. 3 is a sectional view taken along line 3-3 in FIG. 1, FIG. 4 is a top perspective view of the piston, FIG. 5 is a sectional view taken along line 5-5 in FIG. 3, and FIG. FIG. 7 is a sectional view taken along line -7, FIG. 7 is a sectional view taken along line 7-7 of FIG. 3, FIG. 8 is a sectional view of the cavity after correction, and corresponds to FIG. FIG. 10 is a diagram corresponding to FIG. 6, FIG. 10 is an explanatory diagram of a virtual cavity section, and FIG. 11 shows the rate of change in volume of the cavity section when the direction of the cavity section is changed in the circumferential direction. FIG. 12 is a view taken in the direction of the arrow 12 in FIG. 1, and FIG. 13 is a view showing a cooling channel, an oil supply passage, and an oil discharge passage of the piston. Figure 14 is a 14A-14A line cross-sectional view and 14B-14B line sectional view of FIG. 13.

  As shown in FIGS. 1 to 3, the direct fuel injection type diesel engine includes a piston 13 slidably fitted into a cylinder 12 formed in a cylinder block 11, and the piston 13 includes a piston pin 14 and a piston 13. It is connected to a crankshaft (not shown) via a connecting rod 15. Two intake valve holes 17, 17 facing the top surface of the piston 13 and two exhaust valve holes 18, 18 are opened on the lower surface of the cylinder head 16 coupled to the upper surface of the cylinder block 11. The intake port 19 communicates with the intake valve holes 17, 17, and the exhaust port 20 communicates with the exhaust valve holes 18, 18. The intake valve holes 17 and 17 are opened and closed by intake valves 21 and 21, and the exhaust valve holes 18 and 18 are opened and closed by exhaust valves 22 and 22. A fuel injector 23 is provided so as to be positioned on the piston central axis Lp, and a glow plug 24 is provided adjacent to the fuel injector 23.

  As apparent from FIGS. 1 and 4, the top surface of the piston 13 and the lower surface of the cylinder head 16 facing the piston 13 are not flat but inclined in a pent roof shape having a triangular cross section. As a result, the intake valve holes 17 and 17 and the exhaust valve holes 18 and 18 can be ensured in diameter and the intake efficiency and exhaust efficiency can be increased.

  A cavity 25 centered on the piston center axis Lp is recessed in the top surface of the piston 13. On the radially outer side of the cavity 25, a pair of inclined surfaces 13 b, 13 b that incline downward from the top portions 13 a, 13 a extending linearly in parallel with the piston pin 14 toward the intake side and the exhaust side, and inclined surfaces 13 b, 13 b A pair of flat surfaces 13c, 13c that are formed in the vicinity of the lower end of the cylinder and orthogonal to the piston center axis Lp, and a pair of cutout portions 13d, 13d in which both ends of the top portions 13a, 13a are cut out flat are formed.

  The fuel injectors 23 arranged along the piston center axis Lp send fuel in six directions spaced at 60 ° intervals in the circumferential direction around a fuel injection point Oinj, which is a virtual point on the piston center axis Lp. Spray. Of the six fuel injection shafts, two first fuel injection shafts Li1 overlap with the piston pin 14 when viewed in the direction of the piston center axis Lp, and the other four second fuel injection shafts Li2 It intersects with the direction of the pin 14 at an angle of 60 °. Further, the six first and second fuel injection shafts Li1 and Li2 are inclined obliquely downward as viewed in a direction perpendicular to the piston center axis Lp, and the downward degree is small for the first fuel injection shaft Li1. The second fuel injection shaft Li1 is large (see FIGS. 6 and 7).

  The fuel injection point at which the fuel injector 23 actually injects fuel is slightly shifted radially outward from the piston center axis Lp, but the fuel injection point Oinj is determined by the first and second fuel injection shafts Li1 and Li2. It is defined as a point that intersects the piston center axis Lp.

  Next, the cross-sectional shape of the cavity 25 of the invention of the prior application (see Japanese Patent Application Laid-Open No. 2008-002443) will be described in detail with reference to FIGS. The reason for explaining the cross-sectional shape of the cavity 25 of the prior invention is that the cross-sectional shape of the cavity 25 of the present invention is obtained by correcting the cross-sectional shape of the cavity 25 of the prior invention. 5 is a cross section in a direction orthogonal to the piston pin 14, and FIG. 6 is a cross section in a direction crossing the piston pin 14 at 60 ° (cross section including the second fuel injection axis Li2). Is a cross section in the direction along the piston pin 14 (cross section including the first fuel injection axis Li1).

  The invention of the prior application aims at matching the shape of the cavity 25 as much as possible in an arbitrary cross section passing through the piston central axis Lp. The cross-sectional shape of the cavity 25 is divided into two left and right parts with the piston central axis Lp in between, and the two parts are connected in a straight line in the cross section in the direction of the piston pin 14 in FIG. The cross section in the direction orthogonal to the pin 14 and the cross section in the direction intersecting with the piston pin 14 of FIG. 6 at 60 ° are connected in a mountain shape according to the pent roof shape of the piston 13. However, the shape of the main portion of the cross-sectional shape of the cavity 25, that is, the shape shown by hatching in FIGS.

  As is apparent from FIGS. 5 to 7, the cavity 25 formed around the piston center axis Lp has a circumferential wall portion 25 a extending linearly downward from the top surface of the piston 13, and a piston center from the lower end of the circumferential wall portion 25 a. A curved wall portion 25b that curves in a concave shape toward the axis Lp, a bottom wall portion 25c that linearly extends obliquely upward from the radial inner end of the curved wall portion 25b toward the piston central axis Lp, and a piston central axis Lp The top portion 25d is continuous with the radially inner end of the bottom wall portion 25c.

  Lines extending downward and parallel to a distance Ha from lines L-R1 and L-R2 indicating the lower surface of the cylinder head 16 facing the cavity 25 are defined as piston top surface basic lines L-a1 and L-a2. Similarly, lines extending downward in parallel by a distance Hbc from the lines L-R1 and L-R2 indicating the lower surface of the cylinder head 16 are defined as cavity bottom surface basic lines L-bc1 and L-bc2, and the lower surface of the cylinder head 16 is illustrated. The lines extending downward in parallel from the lines L-R1 and L-R2 by a distance Hd are defined as cavity top basic lines L-d1 and L-d2.

  Intersections between an arc having a radius Ra centered on the fuel injection point Oinj and the piston top surface basic lines L-a1, L-a2 are defined as a1, a2. Similarly, the intersections of the arc of radius Rb centered on the fuel injection point Oinj and the cavity bottom surface basic lines L-bc1, L-bc2 are b1, b2, and the arc of radius Rc centered on the fuel injection point Oinj The intersections of the cavity bottom basic lines L-bc1 and L-bc2 are c1 and c2, and the intersection of the arc having a radius Rd centered on the fuel injection point Oinj and the cavity top basic lines Ld1 and Ld2 is d1. , D2. The intersections e1 and e2 are points where perpendiculars drawn from the intersections d1 and d2 to the piston top surface basic lines L-a1 and L-a2 intersect the piston top surface basic lines L-a1 and L-a2.

  The peripheral wall portion 25a of the cavity 25 is above the straight lines a1b1 and a2b2, the bottom wall portion 25c of the cavity 25 coincides with the straight lines c1d1 and c2d2, and the curved wall portion 25b of the cavity 25 has the straight lines a1b1 and a2b2 and the straight lines c1d1 and c2d2. Connect smoothly.

  Thus, the shape of the cavity 25 is set so that the shaded cross-sectional shape determined by the intersection points a1, c1, d1, e1 or the intersection points a2, c2, d2, e2 is equal in any cross-section passing through the piston central axis Lp. Is done.

  The intersection points a1 and a2 correspond to the first specific point An of the present invention, the intersection points e1 and e2 correspond to the second specific point Bn of the present invention, and the intersection points d1 and d2 correspond to the third specific point Cn of the present invention. It corresponds to.

  6 and FIG. 7, the cross section passing through the first and second fuel injection shafts Li1 and Li2 is shown in FIG. 6 as a shaded portion in the cross section in the direction of the piston pin 14 (fuel injection cross section S1). The shaded portion in the cross section (fuel injection cross section S2) in the direction intersecting with the piston pin 14 at 60 ° has the same shape.

  In the cross section in the direction of the piston pin 14 shown in FIG. 7, the point where the first fuel injection axis Li1 intersects the cavity 25 is defined as the fuel collision point P1, and the cross section in the direction intersecting the piston pin 14 shown in FIG. , A point where the second fuel injection axis Li2 intersects the cavity 25 is defined as a fuel collision point P2. The two fuel collision points P1 and P2 exist at the same position on the cross-section of the same shape shaded. Accordingly, the position of the fuel collision point P2 is lower than the position of the fuel collision point P1, and the second fuel injection shaft Li2 extending from the fuel injection point Oinj injects fuel further downward than the first fuel injection shaft Li1. Become.

  A distance D1 from the fuel injection point Oinj to the fuel collision point P1 is substantially equal to a distance D2 from the fuel injection point Oinj to the fuel collision point P2. The fuel collision angle α1 formed by the tangent line of the cavity 25 at the fuel collision point P1 and the first fuel injection axis Li1 is the fuel collision angle α2 formed by the tangent line of the cavity 25 at the fuel collision point P2 and the second fuel injection axis Li2. It almost agrees.

  As described above, according to the invention of the prior application, in an arbitrary cross section passing through the piston center axis Lp, except for a very small part in the vicinity of the fuel injection point Oinj (a region surrounded by the intersections e1, d1, d2, and e2). The cross-sectional shapes of the cavities 25 are the same. In particular, the two cross sections including the first and second fuel injection axes Li1 and Li2 (see FIGS. 6 and 7) have the same cross-sectional shape of the cavity 25, and the fuel injection point in the two cross sections. Since the distances D1, D2 from Oinj to the fuel collision points P1, P2 are set to be approximately equal, and the fuel collision angles α1, α2 at the fuel collision points P1, P2 are set to be approximately equal, air and fuel in each part of the cavity 25 It is possible to make the mixed state uniform in the circumferential direction and improve the combustion state of the air-fuel mixture to increase the engine output and reduce harmful exhaust substances.

  Also, in the cross section where the top surface of the piston 13 shown in FIGS. 5 and 6 is inclined, the angle formed by the edge of the opening of the cavity 25 (intersection point a2) is flat when the top surface of the piston 13 shown in FIG. 7 is flat. Therefore, the heat load of the portion can be reduced and the heat resistance can be improved.

  In the prior invention, the cross-sectional shape of the cavity 25 in FIGS. 5 to 7 is completely the same in the shaded portion, but the intersection points e1, d1, d2, e2 near the fuel injection point Oinj. There is a mismatch in the white area surrounded by. The reason is that the two portions sandwiching the piston central axis Lp of the cross-sectional shape of the cavity 25 are connected in a straight line in the cross section in the direction of the piston pin 14 in FIG. 7, but the cross section in the direction orthogonal to the piston pin 14 in FIG. 6 and the cross section in the direction intersecting with the piston pin 14 at 60 ° in FIG. 6 are connected in a mountain shape according to the pent roof shape of the piston 13, and thus are surrounded by intersection points e 1, d 1, d 2, e 2. The area of the white area is the largest in the cross section in the direction of the piston pin 14 in FIG. 7, decreases in the cross section in a direction intersecting with the piston pin 14 in FIG. 6 at 60 °, and is orthogonal to the piston pin 14 in FIG. This is because it further decreases in the cross section.

  This embodiment is based on the cross-sectional shape of the cavity 25 in the direction of the piston pin 14 (see FIG. 7) where the area of the white area surrounded by the intersections e1, d1, d2, and e2 is maximized, and other directions. Is corrected in the direction of expanding the cross-sectional shape (that is, the direction in which the depth of the cavity 25 is increased) to compensate for the difference in the area of the white area surrounded by the intersections e1, d1, d2, and e2. In this way, the air and fuel are mixed more uniformly in the cross section of the cavity 25 in all directions.

  FIG. 8 illustrates a method for correcting the cross-sectional shape of the cavity 25 in the direction orthogonal to the piston pin 14 of FIG. 5, the shape of the chain line indicates that of the prior invention, and the shape of the solid line indicates that of the present embodiment. Is shown.

  The correction of the cross-sectional shape of the cavity 25 according to the present embodiment increases the area of the shaded portion by moving the positions of the intersection b1 and the intersection c1 downward so as to become the intersection b1 ′ and the intersection c1 ′, respectively. Is done.

  First, the intersection point between the cavity bottom surface basic line L-bc1 and the line extending downward from the straight line e1d1 is determined as f1. Subsequently, the cavity bottom surface basic line L-bc1 passing through the intersection point f1 is rotated downward by a predetermined angle β around the intersection point f1 to set a new cavity bottom surface basic line L-bc1 ′. Subsequently, an intersection point between the arc having the radius Rb centered on the fuel injection point Oinj and the new cavity bottom basic line L-bc1 ′ is determined as the b1 ′, and the arc having the radius Rc centered on the fuel injection point Oinj is newly determined. The intersection point with the cavity bottom surface basic line L-bc1 'is determined as c1'.

  Thus, in the cross-sectional shape of the cavity 25 after the correction, the peripheral wall portion 25a of the cavity 25 is on the straight line a1b1 ′, the bottom wall portion 25c of the cavity 25 coincides with the straight line c1′d1, and the curved wall portion of the cavity 25 is obtained. 25b smoothly connects the straight line a1b1 'and the straight line c1'd1.

  An intersection between the cavity bottom surface basic line L-bc1 and the piston center axis Lp is defined as f, and the cavity bottom surface basic line L-bc1 is rotated downward by a predetermined angle β about the intersection point f to obtain a new cavity bottom surface. The basic line L-bc1 ′ may be set.

  Thus, of the path AnCn on the inner wall surface of the cavity 25, the section from the lowest part of the path AnCn to the third specific point Cn is close to the second fuel injection axis Li2, but by changing the shape of the section Combustion deterioration can be prevented by suppressing the adhesion of fuel to the inner wall surface of the cavity 25.

  In the present embodiment, the net average effective pressure NMEP is improved by about 2% with respect to the prior application invention in a state where no soot is generated.

  FIG. 9 illustrates a method for correcting the cross-sectional shape of the cavity 25 in the direction intersecting with the piston pin 14 of FIG. 6 at 60 °. The shape of the chain line indicates that of the prior invention, and the shape of the solid line. Indicates the present embodiment.

  FIG. 7 (in the direction of the piston pin 14) compared to the difference in the area of the white area surrounded by the intersections e1, d1, d2, e2 in FIG. 7 (in the direction of the piston pin 14) and FIG. 5 (in the direction orthogonal to the piston pin 14). 6 and FIG. 6 (direction intersecting with the piston pin 14 at 60 °) are small, the sectional shape of the cavity 25 is enlarged in FIG. 9 (direction intersecting with the piston pin 14 at 60 °). The amount is smaller than the amount of expansion of the cross-sectional shape of the cavity 25 in FIG. 8 (the direction orthogonal to the piston pin 14).

  Although the correction of the cross-sectional shape of the cavity 25 on one side of the piston central axis Lp has been described above, the correction of the cross-sectional shape of the cavity 25 on the other side of the piston central axis Lp is performed in exactly the same manner.

  As described above, according to the present embodiment, the problems of the prior invention, that is, the cross-sectional shapes of the cavities 25 in the region surrounded by the intersections e1, d1, d2, e2 in the vicinity of the fuel injection point Oinj. Since the mismatch is compensated, the air and fuel mixing state in each part of the cavity 25 is made more uniform in the circumferential direction, and the combustion state of the air-fuel mixture is improved to further increase the engine output and further reduce exhaust harmful substances. Can be achieved.

  FIG. 10 is an explanatory diagram that captures correction of the cross-sectional shape of the cavity 25 according to the present embodiment from another viewpoint.

  In the figure, six half planes X1 to X6 extend radially from a piston central axis Lp passing through the center of the cavity 25. The angles (sandwich angles) formed by two adjacent half-planes X1 to X6 are all 60 °, and the six bisectors that bisect each half-plane X1 to X6 are the piston center axis Lp. , The first and second fuel injection shafts Li1 and Li2 overlap. The cavity 25 is divided into six virtual cavity sections 25A to 25F by six half planes X1 to X6. According to this embodiment, six cavities 25 are corrected by correcting the cross-sectional shape of the cavity 25 described above. It is possible to theoretically set the volumes of the cavity sections 25A to 25F to be the same.

  However, it is not necessary to set the volumes of the six cavity sections 25A to 25F to be completely the same, and even if they are set to be substantially the same, the mixed state of the fuel can be improved as compared with the invention of Patent Document 1 or the prior invention. It can be made more uniform in the circumferential direction. Specifically, the volume variation of the six cavity sections 25A to 25F, that is, the difference between the maximum volume cavity section and the minimum volume cavity section should be made smaller than that of the invention of Patent Document 1 or the prior application invention. In this case, the mixed state of the fuel can be made uniform in the circumferential direction.

  FIG. 11 shows a range of 60 ° to the left and right around the piston center axis Lp, with the direction of the cavity section (that is, the direction of the bisector of the sandwich angle of the cavity section) as the direction of the piston pin 14 (0 °). It shows the rate of change of the volume of the cavity section when moved by. The broken line corresponds to the conventional example (the invention of Patent Document 1), and the solid line corresponds to the present embodiment.

  In either case, the direction of the bisector of the sandwich angle of the cavity section intersects with the direction of the piston pin 14 at 60 ° (see the cavity sections 25B, 25C, 25E, and 25F in FIG. 10). The rate of change at that time is 0%. In the conventional example indicated by the broken line, when the direction of the bisector of the sandwich angle of the cavity section coincides with the direction of the piston pin 14 (see the cavity sections 25A and 25D in FIG. 10), the rate of change is 7% at the maximum. However, in the embodiment indicated by the solid line, the rate of change is maximized at the same position, but the value is greatly reduced to a value of only 0.5%.

  As shown in FIGS. 1 and 12 to 14, an annular cooling channel 26 is formed in the piston 13 so as to be close to the back of the cavity 25. The cooling channel 26 is formed in an annular shape so as to surround the piston center axis Lp when viewed in the piston center axis Lp direction, and the cross-sectional shape thereof is a vertically long oval or elliptical shape and is constant in the circumferential direction. The cooling channel 26 undulates along the shape of the top surface of the piston 13, and the shortest distance d between the cooling channel 26 and the cavity 25 is the same at any position in the circumferential direction.

  The cooling channel 26 is wavy so as to be the highest in the direction of the piston pin axis L2 and the lowest in the direction perpendicular to the piston pin axis L2, but is inclined with respect to the intermediate inclined portion, that is, the piston pin axis L2. From the direction, two oil supply passages 27, 27 arranged at diagonal positions and two oil discharge passages 28, 28 arranged at other diagonal positions are formed downward. On the other hand, two oil jets 30, 30 are provided upward in the cylinder block 29, and these oil jets 30, 30 are directed toward the lower end openings of the two oil supply passages 27, 27. To do.

  Thus, the oil jetted from the oil jets 30, 30 flows upward from the lower ends of the oil supply passages 27, 27 of the piston 13, reaches the cooling channel 26, and changes the flow in the circumferential direction. At this time, since the oil supply passages 27 and 27 are connected to the inclined portion of the cooling channel 26, most of the oil is obliquely upward toward the piston pin axis L2 direction in which the angle formed with the oil supply passages 27 and 27 is an obtuse angle. Thus, only a part of the oil flows obliquely downward in the direction orthogonal to the piston pin axis L2, and the oil branched into two branches is discharged from the two oil discharge passages 28 and 28. While the oil flows through the cooling channel 26, the high-temperature piston 13 is cooled.

  At this time, the position where the oil supply passages 27 and 27 are connected to the inclined portion of the cooling channel 26 is biased to the lower side than the intermediate height position of the inclined portion, so A relatively large amount of oil that branches toward the higher portion of the inclined portion of the 26 flows through the cooling channel 26 over a relatively long distance to a position continuous with the upper ends of the oil discharge passages 28 and 28. The cooling effect of the piston 13 by oil can be enhanced. Even if the top surface of the piston 13 is undulated, the cooling channel 26 is also undulated so that the distance from the cavity 25 is a constant shortest distance d in the circumferential direction. can do. Moreover, since the cross-sectional shape of the cooling channel 26 is constant in the circumferential direction, the flow rate of oil flowing therethrough is constant, and the entire piston 13 can be cooled more evenly.

  Since the oil supply passages 27 and 27 are connected to the inclined portion of the cooling channel 26, the oil flows in the cooling channel 26 in a predetermined direction at a predetermined ratio, and the piston 13 can be cooled more uniformly. it can. If the oil supply passages 27 and 27 are provided at the highest position or the lowest position of the cooling channel 26, when the oil reaches the cooling channel 26 from the oil supply passages 27 and 27 and bifurcates in the circumferential direction. In addition, in which direction and in which ratio the flow becomes unstable, there is a possibility that the cooling of the piston 13 becomes uneven.

  Next, a second embodiment of the present invention will be described based on FIG. 15 and FIG.

  In the first embodiment, the cross-sectional shape of the cooling channel 26 is constant in the circumferential direction, whereas the cooling channel 26 of the second embodiment has a shortest distance d between its upper portion and the cavity 25 in the circumferential direction. While keeping the direction constant, the lower part is made constant height. That is, the height of the upper portion of the cooling channel 26 is highest in the direction of the piston pin axis L2 and lowest in the direction orthogonal to the piston pin axis L2.

  Also according to the present embodiment, since the shortest distance d between the upper portion of the cooling channel 26 and the cavity 25 is constant in the circumferential direction, the piston 13 can be uniformly cooled in the circumferential direction. Moreover, since the lower part of the cooling channel 26 is flat, not only the flow of oil is smooth and the cooling performance of the piston 13 is improved, but also when the cooling channel 26 is formed with a core when the piston 13 is cast, There is an advantage that the lower end of the core can be easily held.

  Next, third and fourth embodiments of the present invention will be described with reference to FIGS.

  In the first and second embodiments, the cooling channel 26 is formed in an annular shape, but in the third and fourth embodiments, the cooling channels 26 and 26 have two central angles of approximately 180 °. It is separated into arc-shaped parts. An oil supply passage 27 and an oil discharge passage 28 are connected to one end side and the other end side of each arc-shaped cooling channel 26, respectively.

  In the third embodiment, the oil supply passages 27 and 27 are connected to one facing portion side of the two cooling channels 26 and 26, and the oil discharge passage 28 is connected to the other facing portion side of the two cooling channels 26 and 26. , 28 are connected.

  In the fourth embodiment, the oil supply passages 27 and 27 and the oil discharge passages 28 and 28 of the two cooling channels 26 and 26 are arranged at diagonal positions.

  According to these third and fourth embodiments, since there is only one flow path from the oil supply passage 27 to the oil discharge passage 28 as compared with the annular cooling channel 26, the oil in the cooling channels 26, 26 is The flow of is stabilized.

  Next, a fifth embodiment of the present invention will be described with reference to FIGS.

  The fifth embodiment includes a cooling channel 26 (having a flat bottom) having the same shape as that of the second embodiment described above, but the cooling channel 26 is disposed inside the annular hollow pipe 33. Of the one pressure ring 31 and the two oil rings 32, 32 that are partitioned and attached to the piston 13, a wear-resistant ring 33 a that supports the pressure ring 31 is integrally formed on the outer peripheral surface of the hollow pipe 33. Is done. When the piston 13 is cast, the hollow pipe 33 integrally provided with the wear-resistant ring 33a is cast inside.

  According to the fifth embodiment, the cooling channel 26 is defined by using the hollow pipe 33 integrally provided with the wear ring 33 for holding the pressure ring 31, so that the core is not required when the piston 13 is cast. Thus, not only can the number of manufacturing steps be reduced, but also integration with the wear-resistant ring 33a can contribute to a reduction in the number of parts. In addition, since the lower portion of the cooling channel 26 is formed flat and only the upper portion is wavy, the wear-resistant ring 33 a that is required to be flat for supporting the pressure ring 31 is replaced with the flat lower portion of the cooling channel 26. Can be supported without hindrance.

  The embodiments of the present invention have been described above, but various design changes can be made without departing from the scope of the present invention.

  For example, the number of oil jets 30 is not limited to two in the embodiment, and may be one or three or more.

  In the embodiment, the number of the virtual cavity sections 25A to 25F is set to 6 (N = 6), but the number of the cavity sections 25A to 25F may be 2 or more (N is 2 or more natural number).

  At this time, the number of the cavity sections 25A to 25F and the number of the fuel injection shafts do not necessarily need to coincide with each other, but by making them coincide, one fuel injection axis corresponds to one cavity section 25A to 25F. As a result, the mixed state of the fuel can be made uniform in the circumferential direction. If the bisector of the sandwich angle of the cavity sections 25A to 25F is made to coincide with the fuel injection axis, the fuel injection axis is located at the center of one cavity section 25A to 25F, and the fuel mixing state is determined. Further, it can be made uniform.

  In the embodiment, the volume of the virtual cavity sections 25 </ b> A to 25 </ b> F does not include the volume of the portion sandwiched between the top surface of the piston 13 at the top dead center and the bottom surface of the cylinder head 16. The volume up to the opening edge (that is, the volume below the piston top surface basic line L-a1, L-a2) is defined as the volume of the virtual cavity sections 25A to 25F. The same operational effects can be achieved.

  Although the diesel engine has been described in the embodiment, the present invention is not limited to the diesel engine, and can be applied to any type of engine that directly injects fuel into the combustion chamber.

The principal part longitudinal cross-sectional view of the diesel engine which concerns on 1st Embodiment (1-1 sectional view taken on the line of FIG. 12). 2-2 line view of FIG. 3-3 line view of FIG. Top perspective view of piston Sectional view along line 5-5 in FIG. 6-6 sectional view of FIG. Sectional view along line 7-7 in FIG. The figure corresponding to FIG. 5 showing the cross-sectional shape of the cavity after correction The figure corresponding to the above-mentioned Drawing 6 showing the section shape of the cavity after amendment Illustration of virtual cavity division A graph showing the rate of change in volume of the cavity section when the direction of the cavity section is changed in the circumferential direction 12 direction arrow view of FIG. Diagram showing piston cooling channel, oil supply passage and oil discharge passage 14A-14A sectional view and 14B-14B sectional view of FIG. The figure corresponding to the said FIG. 13 based on 2nd Embodiment. 15 is a cross-sectional view taken along line 16A-16A and a cross-sectional view taken along line 16B-16B in FIG. The figure which shows the cooling channel which concerns on 3rd Embodiment, an oil supply channel | path, and an oil discharge channel | path The figure which shows the cooling channel, oil supply channel | path, and oil discharge channel | path which concern on 4th Embodiment. Longitudinal sectional view of a piston according to a fifth embodiment Perspective view of hollow pipe with integral wear ring

Explanation of symbols

13 piston 23 fuel injector 25 cavity 25A-25F cavity section 26 cooling channel 27 oil supply passage 30 oil jet 31 pressure ring (piston ring)
33 Hollow pipe 33a Wear ring d Shortest distance L2 Piston pin axis Lp Piston center axis X1 to X6 Half plane

Claims (6)

A piston (13) whose height in the piston central axis (Lp) direction of the top surface changes in the circumferential direction; a cavity (25) recessed in the center of the top surface of the piston (13); and the cavity (25) A fuel direct injection engine comprising a fuel injector (23) for injecting fuel into the fuel injector,
N is a natural number of 2 or more, and the inner wall surface of the cavity (25) and N half planes (X1 to X6) extending radially from the piston central axis (Lp) and having an equal sandwich angle with each other, When the cavity (25) is divided into N virtual cavity sections (25A to 25F), the volumes of the respective virtual cavity sections (25A to 25F) are substantially equal to each other. ), And a cooling channel (26) for supplying oil to the back of the cavity (25) in the piston (13) is provided in the circumferential direction.
The height of the cooling channel (26) in the piston central axis (Lp) direction is set to a circle so that the shortest distance (d) between the cavity (25) and the cooling channel (26) is substantially uniform in the circumferential direction. A fuel direct injection engine characterized by being changed in the circumferential direction.   The direct fuel injection engine according to claim 1, characterized in that the cross-sectional shape of the cooling channel (26) is substantially the same in the circumferential direction.   2. The direct fuel injection engine according to claim 1, wherein the height of the lower portion of the cooling channel in the direction of the piston central axis (Lp) is substantially the same in the circumferential direction.   The height of the upper portion of the cooling channel (26) in the direction of the piston central axis (Lp) is highest in the direction of the piston pin axis (L2), lowest in the direction perpendicular to the piston pin axis (L2), and A monotonous change between the two directions is provided below the piston (13) in an oil supply passage (27) extending downward from an inclined portion where the height of the cooling channel (26) changes. The direct fuel injection engine according to any one of claims 1 to 3, wherein oil is injected from an oil jet (30).   The said cooling channel (26) is comprised by the hollow pipe (33), The wear-resistant ring (33a) holding a piston ring (31) was integrally formed in the outer peripheral surface, The Claim 3 characterized by the above-mentioned. Fuel direct injection engine.   The cooling channel is separated into two cooling channels (26) across the piston pin axis (L2), and oil is supplied from one end of each cooling channel (26) and discharged from the other end. The direct fuel injection engine according to any one of claims 1 to 4, wherein the direct fuel injection engine is provided.

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